$OpenBSD: patch-config_h_in,v 1.1 2017/05/17 16:03:32 espie Exp $

Index: config.h.in
--- config.h.in.orig
+++ config.h.in
@@ -291,6 +291,8 @@
 
 /* Namespace (on non-obj-c files) */
 #ifndef __IN_OBJC_FILE__
+/* prevent clang from complaining about premature namespace */
+#include <iosfwd>
 using namespace std;
 #define __STL_USE_NAMESPACES
 #endif
